mtd: uboot: search for an equivalent MTD name with the mtdids

Using an MTD device (resp. partition) name in mtdparts is simple and
straightforward. However, for a long time already, another name was
given in mtdparts to indicate a device (resp. partition) so the
"mtdids" environment variable was created to do the match.

Let's create a function that, from an MTD device (resp. partition)
name, search for the equivalent name in the "mtdparts" environment
variable thanks to the "mtdids" string.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>

include/linux/mtd/mtd.h

@@ -549,5 +549,10 @@ int mtd_arg_off_size(int argc, char *const argv[], int *idx, loff_t *off,
 void mtd_get_len_incl_bad(struct mtd_info *mtd, uint64_t offset,
 			  const uint64_t length, uint64_t *len_incl_bad,
 			  int *truncated);
+
+/* drivers/mtd/mtd_uboot.c */
+int mtd_search_alternate_name(const char *mtdname, char *altname,
+			      unsigned int max_len);
+
 #endif
 #endif /* __MTD_MTD_H__ */